Capacitance type transducer and acoustic sensor

Abstract

A capacitance type transducer has a substrate with an opening on a surface thereof, a back plate arranged to oppose the opening of the substrate, and a vibrating electrode film arranged to oppose the back plate across a gap between the vibrating electrode film and the back plate. The capacitance type transducer converts a displacement of the vibrating electrode film into a change in capacitance between the vibrating electrode film and the back plate. The capacitance type transducer has a pressure releasing flow channel which is an air flow channel formed by a gap between a part of the vibrating electrode film and a protruding portion integrally provided on the back plate.

The invention claimed is: 
     
       1. A capacitance type transducer, comprising:
 a substrate with an opening on a surface thereof; 
 a back plate arranged to oppose the opening of the substrate; and 
 a vibrating electrode film arranged to oppose the back plate across a gap between the vibrating electrode film and the back plate, 
 wherein the capacitance type transducer converting a displacement of the vibrating electrode film into a change in capacitance between the vibrating electrode film and the back plate, and 
 wherein the capacitance type transducer further comprises a pressure releasing flow channel which is an air flow channel formed by a gap between a part of the vibrating electrode film and a protruding portion integrally provided on the back plate so as to penetrate into or cover a hole of the vibrating electrode film or so as to face towards an end surface of the vibrating electrode film and which is configured to, when the vibrating electrode film deforms under pressure, release the pressure applied to the vibrating electrode film by increasing a flow channel area due to a relative movement of the vibrating electrode film and the protruding portion integrally provided on the back plate. 
 
     
     
       2. The capacitance type transducer according to  claim 1 , wherein
 at least a part of a peripheral section of the back plate bends to form a side surface and the back plate is fixed to the substrate in a tip section of the side surface, 
 the pressure releasing flow channel is formed by a gap between an end surface of the vibrating electrode film and a protruding portion integrally formed on the side surface of the back plate, and 
 when the vibrating electrode film deforms under pressure, the pressure applied to the vibrating electrode film is released by increasing the gap between the end surface of the vibrating electrode film and the side surface of the back plate as the end surface of the vibrating electrode film and the protruding portion formed on the side surface of the back plate relatively move and deviate. 
 
     
     
       3. A capacitance type transducer, comprising:
 a substrate with an opening on a surface thereof; 
 a back plate arranged to oppose the opening of the substrate; and 
 a vibrating electrode film arranged to oppose the back plate across a gap between the vibrating electrode film and the back plate, 
 wherein the capacitance type transducer converts a displacement of the vibrating electrode film into a change in capacitance between the vibrating electrode film and the back plate, 
 wherein the capacitance type transducer further comprises a pressure releasing flow channel which is an air flow channel formed by a gap between a part of the vibrating electrode film and a protruding portion integrally provided on the back plate and which is configured to, when the vibrating electrode film deforms under pressure, release the pressure applied to the vibrating electrode film by increasing a flow channel area due to a relative movement of the vibrating electrode film and the protruding portion integrally provided on the back plate, 
 wherein the protruding portion is a protruding pillar structure, 
 wherein the pressure releasing flow channel is formed by a gap between a hole provided in the vibrating electrode film and a protruding pillar structure integrally provided from the back plate to a side of the vibrating electrode film, 
 wherein at least a tip section of the protruding pillar structure has a smaller diameter than a diameter of the hole and the protruding pillar structure penetrates into the hole in a state prior to the vibrating electrode film deforming under pressure, and 
 wherein, when the vibrating electrode film deforms under pressure, the pressure applied to the vibrating electrode film is released as the vibrating electrode film and the protruding pillar structure of the back plate relatively move and the penetration of the protruding pillar structure into the hole is canceled. 
 
     
     
       4. A capacitance type transducer, comprising:
 a substrate with an opening on a surface thereof; 
 a back plate arranged to oppose the opening of the substrate; and 
 a vibrating electrode film arranged to oppose the back plate across a gap between the vibrating electrode film and the back plate, 
 wherein the capacitance type transducer converts a displacement of the vibrating electrode film into a change in capacitance between the vibrating electrode film and the back plate, 
 wherein the capacitance type transducer further comprises a pressure releasing flow channel which is an air flow channel formed by a gap between a part of the vibrating electrode film and a protruding portion integrally provided on the back plate and which is configured to, when the vibrating electrode film deforms under pressure, release the pressure applied to the vibrating electrode film by increasing a flow channel area due to a relative movement of the vibrating electrode film and the protruding portion integrally provided on the back plate, 
 wherein the protruding portion is a protruding pillar structure, 
 wherein the pressure releasing flow channel is formed by a gap between a hole provided in the vibrating electrode film and a protruding pillar structure integrally provided from the back plate to a side of the vibrating electrode film, 
 wherein the protruding pillar structure has a larger diameter than a diameter of the hole and a tip of the protruding pillar structure covers the hole from a side of the back plate in a state prior to the vibrating electrode film deforming under pressure, and 
 wherein, when the vibrating electrode film deforms under pressure, the pressure applied to the vibrating electrode film is released as the vibrating electrode film and the protruding pillar structure of the back plate relatively move and the tip of the protruding pillar structure separates from the hole. 
 
     
     
       5. The capacitance type transducer according to  claim 3 , wherein in a state prior to the vibrating electrode film deforming under pressure, the protruding pillar structure penetrates through the hole and the tip of the protruding pillar structure is positioned on an opposite side of the vibrating electrode film to the back plate. 
     
     
       6. The capacitance type transducer according to  claim 3 , wherein a diameter of the protruding pillar structure either increases from the tip of the protruding pillar structure toward the back plate or is constant. 
     
     
       7. The capacitance type transducer according to  claim 3 , wherein the protruding pillar structure is formed by a same film forming process as that of the back plate. 
     
     
       8. The capacitance type transducer according to  claim 1 , wherein the vibrating electrode film is fixed to the substrate at an anchor section and the vibrating electrode film is not in contact with the substrate and the back plate at locations other than the anchor section. 
     
     
       9. The capacitance type transducer according to  claim 1 , wherein the back plate has a plurality of perforations. 
     
     
       10. The capacitance type transducer according to  claim 3 , wherein the substrate is arranged to avoid a portion opposing the protruding pillar structure integrally provided on the back plate. 
     
     
       11. The capacitance type transducer according to  claim 3 , wherein
 the back plate is arranged to oppose the substrate, and 
 the protruding pillar structure is provided from the back plate toward a side of the substrate, and the tip of the protruding pillar structure is positioned on a same plane as a surface of the substrate on the back plate side or further toward the back plate side than the surface. 
 
     
     
       12. The capacitance type transducer according to  claim 1 , wherein
 the back plate has a stationary electrode film in a central section, and 
 the protruding portion is provided on an outer side of the stationary electrode film on the back plate. 
 
     
     
       13. The capacitance type transducer according to  claim 1 , wherein the protruding portion is provided in a central section of the back plate. 
     
     
       14. The capacitance type transducer according to  claim 6 , wherein a side surface of the protruding pillar structure forms a tapered surface and an inclination angle of the tapered surface with respect to the back plate is set to 60 degrees or more and 85 degrees or less. 
     
     
       15. The capacitance type transducer according to  claim 3 , wherein
 the vibrating electrode film has an approximately rectangular shape and is fixed at fixing sections provided in four corners of the vibrating electrode film, and 
 the protruding portion is provided at four locations in portions of the back plate which correspond to the four corners of the vibrating electrode film and to a further inner side than the fixing sections in a plan view. 
 
     
     
       16. The capacitance type transducer according to  claim 13 , wherein the protruding portion is provided at one location in a central section of the back plate. 
     
     
       17. The capacitance type transducer according to  claim 15 , wherein the protruding portion is further provided at four locations in portions of the back plate, which correspond to central sections of four sides of the vibrating electrode film in a plan view, so as to be provided at a total of eight locations. 
     
     
       18. The capacitance type transducer according to  claim 17 , wherein the protruding portion is further provided at one location in the central section of the back plate so as to be provided at a total of nine locations. 
     
     
       19. The capacitance type transducer according to  claim 3 , wherein in a state where the protruding pillar structure has penetrated into the hole before the vibrating electrode film deforms under pressure, the gap between the protruding pillar structure and the hole is set to 0.2 μm or more and 20 μm or less on one side. 
     
     
       20. The capacitance type transducer according to  claim 3 , wherein the back plate includes a stationary electrode film positioned to avoid a location where the protruding portion is provided in a plan view, and a distance between the protruding portion and the stationary electrode film is set to 1 μm or more and 15 μm or less. 
     
     
       21. The capacitance type transducer according to  claim 3 , wherein a size of the gap between the back plate and the vibrating electrode film is set larger within a prescribed range in a periphery of the protruding portion, as compared to outside of the prescribed range. 
     
     
       22. The capacitance type transducer according to  claim 3 , wherein a size of a sound hole in the back plate is set smaller within a prescribed range in a periphery of the protruding portion, as compared to outside of the prescribed range. 
     
     
       23. The capacitance type transducer according to  claim 3 , wherein a sound hole within a prescribed range in a periphery of the protruding portion of the back plate and a hole provided in the vibrating electrode film are arranged so that at least parts thereof overlap with each other in a plan view. 
     
     
       24. An acoustic sensor comprising the capacitance type transducer according to  claim 1 , wherein the acoustic sensor converts sound pressure into a change in capacitance between the vibrating electrode film and the back plate and detects the capacitance change. 
     
     
       25. An acoustic sensor comprising the capacitance type transducer according to  claim 2 , wherein the acoustic sensor converts sound pressure into a change in capacitance between the vibrating electrode film and the back plate and detects the capacitance change. 
     
     
       26. An acoustic sensor comprising the capacitance type transducer according to  claim 3 , wherein the acoustic sensor converts sound pressure into a change in capacitance between the vibrating electrode film and the back plate and detects the capacitance change. 
     
     
       27. An acoustic sensor comprising the capacitance type transducer according to  claim 4 , wherein the acoustic sensor converts sound pressure into a change in capacitance between the vibrating electrode film and the back plate and detects the capacitance change.